Method and system to transport high-quality video signals

ABSTRACT

Society of Motion Picture and Television Engineers (SMPTE) video data is separated into first data and second data. A first signal is formed based on the first data. A second signal is formed based on the second data. The first signal is transported via a first Optical Carrier 3 (OC-3) channel. The second signal is transported via a second OC-3 channel.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 09/956,475, filed Sep. 18, 2001, now U.S. Pat. No. 7,110,412,the entirety of which is hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to methods and systems for transportinghigh-quality video signals.

BACKGROUND

The video industry has adopted the Society of Motion Picture andTelevision Engineers (SMPTE) 259M (level C) standard almost exclusivelyfor high quality video in studio and production applications. In someapplications, a SMPTE 259M signal is to be transported to a remotelocation, which may be several miles away for example. Current methodsof transporting SMPTE 259M signals or other professional quality videosignals to remote locations use either dark fiber overlay networks orproprietary methods over very high bandwidth pipes. For example, anOC-12 channel may be used to transport an SMPTE 259M signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is pointed out with particularity in the appended claims.However, other features of the invention will become more apparent andthe invention will be best understood by referring to the followingdetailed description in conjunction with the accompanying drawings inwhich:

FIG. 1 is a block diagram of an embodiment of a system to transporthigh-quality video;

FIG. 2 is a flow chart of an embodiment of a method performed at atransmitter end;

FIG. 3 is a flow chart of an embodiment of a method performed at areceiver end;

FIG. 4 illustrates the SMPTE 259M data structure;

FIG. 5 is a block diagram illustrating an embodiment of an uncompressedsignal based on a subframe of a SMPTE frame;

FIG. 6 is a schematic block diagram of an embodiment of a videoprocessor at the transmitter end;

FIG. 7 is a schematic block diagram of an embodiment of a videoprocessor at the receiver end;

FIG. 8 is a block diagram of an embodiment of a system to provide timinginformation;

FIG. 9 is a block diagram of an embodiment of a system to reconstructthe timing information at the receiver end; and

FIG. 10 is a block diagram depicting a packing method for transmitting10-bit word information using 8-bit bytes.

DETAILED DESCRIPTION OF THE DRAWINGS

Briefly, embodiments of the present invention provide an improvedprocess for transporting high-quality video. The process includesseparating the video data into two sets of data, encapsulating each setof data into asynchronous transfer mode (ATM) cells, and transportingtwo ATM cell-based bit streams over dual, concatenated Optical Carrier 3(OC-3) channels. Error checking and/or correction is used to reduce theprobability of data errors during transport.

Embodiments of the present invention are described with reference toFIG. 1, which is a block diagram of an embodiment of a system totransport high-quality video, FIG. 2, which is a flow chart of anembodiment of a method performed at a transmitter end 20, and FIG. 3,which is a flow chart of an embodiment of a method performed at areceiver end 22.

As indicated by block 24, the method comprises separating SMPTE videodata 26, such as SMPTE 259M video data, into first uncompressed data 30and second uncompressed data 32. Preferably, the act of separating theSMPTE video data comprises separating each frame of the SMPTE video datainto a first subframe and a second subframe. The first subframecomprises even lines of active video from the frame, and the secondsubframe comprises odd lines of active video from the frame. In additionto active video, the first subframe and the second subframe may furthercomprise horizontal ancillary data, optional video data and/or verticalancillary data.

The SMPTE 259M standard is inherently suitable to separate video databecause of its field and frame-oriented data structure. In addition,extraneous data can be eliminated since the timing signals are notnecessary to carry along a transport stream.

FIG. 4 illustrates the SMPTE 259M data structure. The data structurecomprises active video fields 34 and 36. The active video fields 34 and36 contain component pixel data. The active video field 34 includes oddlines of active video from a frame, while the active video field 36includes even lines of active video from a frame. Optional video fields40 and 42 contain vertical blanking interval (VBI) data and non-criticaldata. Horizontal ancillary (HANC) data fields 44 and 46 contain audio,timing and control information. Vertical ancillary (VANC) data fields 48and 49 contain special user information. A clear delineation between thefields is created by the inherent timing signals EAV 50 and SAV 52.

The aforementioned structure is exploited to separate the SMPTE videodata into two equal blocks. The first uncompressed data includes datafrom the active video field 34, the HANC data field 44, and a portion ofthe data from the optional video field 40 and/or the VANC data field 48.The second uncompressed data includes data from the active video field36, the HANC data field 46, and a portion of the data from the optionalvideo field 42 and/or the VANC data field 49.

Referring back to FIG. 2, the method comprises acts of forming a firstuncompressed signal based on the first uncompressed data (block 54) andforming a second uncompressed signal based on the second uncompresseddata (block 56). The first uncompressed signal is based on the eachfirst subframe. The second uncompressed signal is based on the eachsecond subframe.

The act of forming the first uncompressed signal further comprisesappending a corresponding first sequence number to each first subframe,and encapsulating each first subframe with its corresponding firstsequence number into at least one asynchronous transfer mode (ATM) cell.Similarly, the act of forming the second uncompressed signal furthercomprises appending a corresponding second sequence number to eachsecond subframe, and encapsulating each second subframe with itscorresponding second sequence number into at least one ATM cell. Thesequence numbers are appended to each subframe since traffic in most ATMnetworks can take any of several paths, each with a potentiallydifferent latency and cell delay variation. The sequence numbers areused at the receiving end 22 to order reconstructed frames.

In one embodiment, each sequence number is defined by 20 bits. One bitof the sequence number is used to identify whether the field is field 1or field 2. Choosing 20 bits for the sequence number field allowssequence numbers up to 2^(20−1)=524,288. For a frame rate of 30 framesper second, the maximum video length for 20 sequence number bits is(524,288 frames)/((30 frames per second)*(3600 seconds per hour)), whichapproximately equals 4.854 hours.

FIG. 5 is a block diagram illustrating an embodiment of an uncompressedsignal which results from the act of either block 54 or block 56 in FIG.2. The uncompressed signal comprises a bit stream including a sequencenumber 60, ancillary data 62, and active video data 64 for a subframefrom a first frame. Thereafter, the bit stream includes a sequencenumber 70, ancillary data 72, and active video data 74 for a subframefrom a second frame. The pattern of including a sequence number,ancillary data and active video data for a subframe is repeated for eachsucceeding frame.

The above-described encapsulation method distinguishes video data (e.g.field/frame data) from ancillary data to facilitate the SMPTE 259M videodata being properly reconstructed at the receiver end 22. Since timingrelationships are well-defined in the SMPTE 259M standard, and since afixed frequency of 270 Mbps is used, logic at the receiver end 22 canadd the proper timing signals.

The bandwidth required to transmit the above bit stream is calculated asfollows. With respect to the active video bandwidth, each field has 244active video lines. The number of words per line is 720 pixels*2(Cr, Y,Cb)=1440. Since each word consists of 10 bits, the number of bits perline is (1440 words per line)*(10 bits per word)=14,400. Thus, the totalnumber of active video bits per field is (14,400 bits per line)*(244active video lines per field)=3.5136 Mb. Since each frame is based on 2fields, the total number of active video bits per frame is (3.5136 Mbper field)*(2 fields per frame)=7.0272 Mb. For a frame rate of 30 framesper second, the active video bit rate is (7.0272 Mb per frame)*(30frames per second)=210.816 Mbps. Accounting for ATM overhead with a celltax of 1.09433, the total active video bandwidth is 1.09433*210.816Mbps=230.7043 Mbps.

The bandwidth for the HANC data is determined as follows. The HANC bitrate is 30 Mbps. Accounting for ATM overhead with a cell tax of 1.09433,the HANC bandwidth is 1.09433*30 Mbps=32.8302 Mbps.

The bandwidth for the VANC/optional data is determined as follows. Eachframe has 20 lines allocated for VANC/optional data. The 20 linescomprise any 10 lines selected from lines 1-20, and any 10 linesselected from lines 264-283. Since the number of bits per line is14,400, the total number of VANC/optional bits per frame is (14,400 bitsper line)*(20 VANC/optional lines per field)=288,000. For a frame rateof 30 frames per second, the VANC/optional bit rate is (288,000 bits perframe)*(30 frames per second)=8.64 Mbps. Accounting for ATM overheadwith a cell tax of 1.09433, the VANC/optional bandwidth is 1.09433*8.64Mbps=9.4550112 Mbps.

The total data rate is equal to the sum of the total active videobandwidth, the HANC bandwidth and the VANC/optional bandwidth. Thus, thetotal data rate is 230.7043 Mbps+32.8302 Mbps+9.4550112 Mbps, whichequals 272.984612 Mbps. This is less than the 299.52 Mbps bandwidthavailable on two OC-3 links. Since the data is separated into twofields, the total data rate per field is 272.984612 Mbps/2, whichapproximately equals 136.4923 Mbps.

Optionally, the act of forming the first uncompressed signal furthercomprises adding a first ATM adaptation layer (AAL) with either an errorchecking code or an error correcting code. Similarly, the act of formingthe second uncompressed signal may optionally comprise adding a secondATM adaptation layer with either an error checking code or an errorcorrecting code. A block coding algorithm such as Reed Solomon oranother forward error correcting (FEC) code may be used.

Referring back to FIGS. 1 and 2, the method comprises transporting 80the first uncompressed signal via a first OC-3 channel 82, andtransporting 84 the second uncompressed signal via a second OC-3 channel86. The OC-3 channels 82 and 86 are provided by an ATM network 90.

The adaptation layers may be added because of additional bandwidthavailable on two OC-3 links beyond the 272.984612 Mbps required by thetwo bit streams. Either AAL-1 with FEC or AAL-5 with FEC may be used.The former is less efficient but more robust, and the latter is moreefficient and slightly less robust. The selection of which of these twoadaptations to use may be dictated by specifications of a specificapplication. Note that the FEC process is symmetrical, requiringprocessing the inverse algorithm at the receiver end 22.

Turning now to FIG. 3, a method performed at the receiver end 22comprises receiving the first uncompressed signal via the first OC-3channel (block 92), and receiving the second uncompressed signal via thesecond OC-3 channel (block 94). As described above, the firstuncompressed signal comprises a bit stream of a first plurality of ATMcells, and the second uncompressed signal comprises a bit stream of asecond plurality of ATM cells. The ATM cells are extracted from theincoming bit streams.

As indicated by blocks 96 and 100, the method optionally comprisesperforming error checking based on the first uncompressed signal, andperforming error checking based on the second uncompressed signal. Aninverse FEC block code algorithm is used for error checking andrecovery. If an error is detected, the block code may provide correctiondepending on which block code is used and the type and number of errors.

As indicated by block 102, the method comprises extracting each firstsubframe and its corresponding first sequence number from the firstplurality of ATM cells. As indicated by block 104, the method comprisesextracting each second subframe and its corresponding second sequencenumber from the second plurality of ATM cells. In these acts, the datapayload is extracted from the AALML-1 or AAL-5 encapsulation.

As indicated by block 106, the method comprises reconstructing SMPTEvideo data 108, such as SMPTE 259M video data. Each frame of the SMPTEvideo data is reconstructed based on a first corresponding subframerepresented within the first uncompressed signal and a secondcorresponding subframe represented within the second uncompressedsignal. Further, the EAV and SAV timing signals are added toreconstructed frames. The reconstructed frames are ordered based on eachfirst sequence number and each second sequence number.

One approach to ordering the frames comprises using a buffer managementprocess to synchronize the arriving data based on the sequence numbers.A modified leaky bucket (LB) algorithm or similar technique can be usedto synchronize the two fields. Optimization can be performed by varyingthe limit parameter based on the LB counter and the last compliancetime. The arrival time is based on the arrival of the sequence number.This allows for a fast implementation in silicon, using the sequencenumber to direct data to the appropriate buffers.

It is noted that some acts described with reference to FIGS. 2 and 3need not be performed in the order shown in FIGS. 2 and 3. Further, someof the acts may be performed concurrently. For example, the act oftransporting the first signal via the first OC-3 channel typically isperformed concurrently with the act of transporting the second signalvia the second OC-3.

Referring back to FIG. 1, the transmitter end 20 comprises a videoprocessor 110 which performs the method described with reference to FIG.2. FIG. 6 is a schematic block diagram of an embodiment of the videoprocessor 110 at the transmitter end 20. Each video frame 120 withinSMPTE 259M video data 122 is separated into two active video subframes.A temporary buffer 124 stores one of the two active video subframes. Atemporary buffer 126 stores the other of the two active video subframes.The temporary buffers 124 and 126 may have equal sizes. Ancillary data130 within the SMPTE 259M video data 122 is appended to outputs of thetemporary buffers 124 and 126. The resulting streams are applied tofirst-in-first-out (FIFOs) 132 and 134. A sequence number is added tothe FIFO stream 132 by tagging logic 136. A sequence number is added tothe FIFO stream 134 by tagging logic 140. An AAL 142 applies FEC to theoutput of the tagging logic 136. An AAL 144 applies FEC to the output ofthe tagging logic 140. A physical layer 146 couples the AAL 142 to theOC-3 channel 82 in FIG. 1. A physical layer 150 couples the AAL 144 tothe OC-3 channel 86 in FIG. 1. The aforementioned components of thevideo processor 110 are directed by system control logic 152.

Referring back to FIG. 1, the receiver end 22 comprises a videoprocessor 158 which performs the method described with reference to FIG.3. FIG. 7 is a schematic block diagram of an embodiment of the videoprocessor 158 at the receiver end 22. A physical layer 160 couples theOC-3 channel 82 in FIG. 1 to an AAL 162. A physical layer 164 couplesthe OC-3 channel 86 in FIG. 1 to an AAL 166. The physical layers 160 and164 extract ATM cells from an incoming bit stream. The MLs 162 and 166perform an inverse FEC block code algorithm for error checking and/orcorrecting, and extract the data payload from AAL-1/5 encapsulation.

Tagging logic 170 is responsive to the AAL 162 to order each subframebased on its sequence number, and to remove the sequence number. Tagginglogic 172 is responsive to the AAL 166 to order each subframe based onits sequence number, and to remove the sequence number. The resultingsynchronized buffers are indicated by FIFOs 174 and 176. Ancillary data180 is extracted from each subframe. Temporary buffers 182 and 184 storethe two active video portions which, when combined with EAV and SAVsignals, form a video frame 186. The video frame 186 is in accordancewith an SMPTE standard such as SMPTE 259M. The aforementioned componentsof the video processor 158 are directed by system control logic 190. Thesystem control logic 190, among other things, directs synchronization ofdata from the two separate fields.

FIG. 8 is a block diagram of an embodiment of a system to provide timinginformation in addition to the sequence number. The timing informationis based upon a first clock 200 and a second clock 202. Preferably, thefirst clock 200 has a frequency of 90 kHz, and the second clock 202 hasa frequency of 27 MHz.

A first counter 204 is responsive to the first clock 200. A secondcounter 206 is responsive to the second clock 202. Preferably, the firstcounter 204 is a 23-bit counter and the second counter 206 is a 9-bitcounter. The timing information has an upper portion 210 comprising bitsfrom the second counter 206, and a lower portion 212 comprising bitsfrom the first counter 204. The timing information is encapsulated asdescribed above for the bit stream. The additional 32 bits keep theoverall bandwidth within the bandwidth limit of the two OC-3 links.

FIG. 9 is a block diagram of an embodiment of a system to reconstructthe timing information at the receiver end. A clock recovery module 214outputs a first clock signal based on the lower portion 212 of thereceived timing information, and a second clock signal based on theupper portion 210. The clock recovery module 214 may be embodied using aphase-locked loop circuit. Preferably, the first clock signal has afrequency of 90 kHz and the second clock signal has a frequency of 27MHz.

The clock signals can be useful in reducing jitter and synchronizingdata. The use of field/frame counters allow better decisions to be madewhen reconstructing frames at the receiver. If link errors occur, thereceiver can perform a first check on field number and decide what to dobased thereupon. For example, the receiver may decide to use a previousframe and wait for the next consecutive frames to resynchronize.

FIG. 10 is a block diagram depicting a packing method for transmitting10-bit word information using 8-bit bytes. Four consecutive pixelsamples 220, 222, 224 and 226 are packed into five consecutive bytes230, 232, 234, 236 and 238.

Several embodiments including preferred embodiments of a method andsystem to transport high-quality video signals have been describedherein.

The herein-described methods and systems facilitate high bandwidth,real-time video signals to be transmitted over existing ATMinfrastructure. Use of two OC-3 links rather than one OC-12 connectiontranslates into a significant savings in bandwidth.

It will be apparent to those skilled in the art that the disclosedinvention may be modified in numerous ways and may assume manyembodiments other than the preferred form specifically set out anddescribed above.

Accordingly, it is intended by the appended claims to cover allmodifications of the invention which fall within the true spirit andscope of the invention.

1. A method comprising: separating a frame of Society of Motion Pictureand Television Engineers (SMPTE) video data into a first subframe and asecond subframe, wherein the first subframe comprises even lines ofactive video and the second subframe comprises odd lines of activevideo; forming a first signal based on the first subframe; forming asecond signal based on the second subframe; transporting the firstsignal via a first Optical Carrier 3 (OC-3) channel; and transportingthe second signal via a second OC-3 channel.
 2. The method of claim 1,wherein the SMPTE video data is SMPTE 259M video data.
 3. The method ofclaim 1, wherein forming the first signal comprises: appending a firstsequence number to the first subframe; and encapsulating the firstsubframe and the first subframe number into at least one asynchronoustransfer mode (ATM) cell.
 4. The method of claim 3, wherein forming thesecond signal comprises: appending a second sequence number to thesecond subframe; and encapsulating the second subframe and the secondsubframe number into at least one ATM cell.
 5. The method of claim 1,wherein the first subframe comprises active video data and ancillarydata, and the second subframe comprises active video data and ancillarydata.
 6. A computer-readable storage medium comprising a set ofinstructions to direct a computer system to perform the acts of:separating a frame of Society of Motion Picture and Television Engineers(SMPTE) video data into a first subframe and a second subframe, whereinthe first subframe comprises even lines of active video and the secondsubframe comprises odd lines of active video; forming a first signalbased on the first subframe; forming a second signal based on the secondsubframe; transporting the first signal via a first Optical Carrier 3(OC-3) channel; and transporting the second signal via a second OC-3channel.
 7. A video processor operative to separate Society of MotionPicture and Television Engineers (SMPTE) video data into first data andsecond data, the video processor comprising: a first ATM adaptationlayer (AAL) operative to form a first signal based on the first data andto couple the first signal to a first Optical Carrier 3 (OC-3) channel,and a second AAL operative to form a second signal based on the seconddata and to couple the second signal to a second OC-3 channel.
 8. Amethod comprising: receiving a first signal via a first Optical Carrier3 (OC-3) channel; receiving a second signal via a second OC-3 channel;and reconstructing at least one frame of Society of Motion Picture andTelevision Engineers (SMPTE) video data based on at least a firstsubframe represented within the first signal and a second subframerepresented within the second signal, wherein the first subframecomprises even lines of active video for the at least one reconstructedframe of SMPTE video data and the second subframe comprises odd lines ofactive video for the at least one reconstructed frame of SMPTE videodata.
 9. The method of claim 8, wherein the SMPTE video data is SMPTE259M video data.
 10. The method of claim 8, wherein the first subframecomprises a first sequence number and the second subframe comprises asecond sequence number, and wherein the at least one frame of SMPTEvideo data is reconstructed based on the first and second sequencenumbers.
 11. The method of claim 10, wherein the first signal comprisesa first plurality of asynchronous transfer mode (ATM) cells and thesecond signal comprises a second plurality of ATM cells.
 12. The methodof claim 11, further comprising: extracting the first subframe and thefirst sequence number from a first ATM cell of the first plurality ofATM cells; and extracting the second subframe and the second sequencenumber from a second ATM cell of second plurality of ATM cells.
 13. Themethod of claim 8, further comprising: performing error checking basedon the first signal; and performing error checking based on the secondsignal.
 14. The method of claim 8, wherein the first subframe comprisesactive video data and ancillary data.
 15. The method of claim 8, whereinat least one of the first and second subframes comprises ancillary data.16. A video processor comprising: a first physical layer operative toreceive a first signal via a first Optical Carrier 3 (OC-3) channel; anda second physical layer operative to receive a second signal via asecond OC-3 channel; wherein the video processor is operative toreconstruct Society of Motion Picture and Television Engineers (SMPTE)video data based on a first subframe and a first sequence number fromthe first signal and a second subframe and a second sequence number fromthe second signal.
 17. The video processor of claim 16, wherein thefirst physical layer is coupled to a first asynchronous transfer modeadaptation layer (AAL) and the second physical layer is coupled to asecond AAL.